I know you have a very fast 64 bit machine

Dream on! My 32-bit machine doesn't even have a virtual second core from hyperthreading.

I'm not sure what my work machine is, but it's also 32-bit.

My earlier run was on my work machine. This is on my work machine too:

This is Perl 5.010000
            Rate  range repeat  isook unpack substr
range   416206/s     --    -6%    -8%   -45%   -67%
repeat  443742/s     7%     --    -1%   -41%   -65%
isook   450082/s     8%     1%     --   -41%   -64%
unpack  756739/s    82%    71%    68%     --   -40%
substr 1257912/s   202%   183%   179%    66%     --

This is Perl 5.010000
            Rate  range repeat  isook unpack substr
range   415726/s     --    -5%    -8%   -47%   -67%
repeat  436462/s     5%     --    -4%   -44%   -65%
isook   454041/s     9%     4%     --   -42%   -64%
unpack  779486/s    88%    79%    72%     --   -38%
substr 1262559/s   204%   189%   178%    62%     --
[download]

(Threaded 32-bit build on linux)

Interesting.